Such friction liners are used in the manufacture of clutch friction plates for motor vehicles, the clutch friction plate being of the kind including a face plate portion which carries at its outer periphery a plurality of friction liners which are distributed around the center of the clutch plate in such a way as to define an annular friction crown.
At each engagement of the clutch, the friction liners become progressively gripped between a pressure plate and a reaction plate of the clutch. Heating which is brought about by the corresponding friction displays differential or uneven thermal expansion, the result of which is that the pressure plate gradually adopts a conical shape. This is illustrated in FIG. 11 of the accompanying drawings, to which reference will be made in more detail later.
The metallic support plates and the friction liners also undergo deformation which gives the liners a curve such that, in the present state of the art, a large reduction develops over the course of time in the mean friction radius between the friction liners of the pressure plate. This leads to a major reduction in overall efficiency of the clutch, and therefore in torque transmission.
In addition, the zone in which the friction liners are subjected to pressure from the pressure plate becomes progressively offset towards the axis of the assembly. This leads to unequal wear of the friction liners and even perhaps the incidence of fracture.